This invention relates to the equipment and methods used in the completion of wells, such as oil and gas wells, and in particular to downhole machining of completion equipment.
Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation (i.e., a xe2x80x9creservoirxe2x80x9d) by drilling a well that penetrates the hydrocarbon-bearing formation. Once a wellbore has been drilled, the well must be xe2x80x9ccompletedxe2x80x9d before hydrocarbons can be produced from the well. A completion involves the design, selection, and installation of tubulars, tools, and other equipment that are located in the wellbore for the purpose of conveying, pumping, or controlling the production or injection of fluids. The maintenance, operation, adaptability, and management of the completion must be considered as well. The completion of a well represents a complex technology that has evolved around the technique and equipment developed for this purpose.
Completion generally includes the installation of casing and one or more tubing strings in the wellbore, cementing, the installation of a variety of downhole equipment, such as packers and flow control devices, and in most cases perforating the casing to allow the hydrocarbons to flow from the formation into the wellbore. It is customary to install completion equipment that is particularly adapted for the specific well involved. Thus, commonly used types of completion equipment, such as landing nipples, packers, and flow control valves, are typically available in a variety of sizes and configurations, so that a particular size and configuration can be selected that will be best suited to work in the well in conjunction with the other equipment that is also installed in that well.
As a more specific example, as part of the completion practice, the control of fluid within the tubing and the flow of fluid from tubing to casing, or vice versa, is an important feature of flow control equipment. In order to properly construct a flow control system, any number of seating locations must be available in which the specified flow control devices can be installed. Landing or seating nipples are distributed throughout the tubing string as a method to locate and latch different flow control mechanisms. These nipples come with a variety of internal diameters and locking recesses in order to properly locate pre-selected equipment in place at the correct depth. When the desired tool is lowered into a well by wireline or the like, co-acting locking means on the tool can engage a corresponding locking recess on the landing nipple. Thus, by using a plurality of landing nipples in a well that have a different inner diameters as well as sizes or shapes of locking recesses, downhole tools can be selectively installed by matching the size and shape of the tool""s locking means to the corresponding locking recess on the desired landing nipple. Significant planning is involved in specifying the correct nipple sequences so that the desired flow-control devices can reach their targets. In addition to the necessary planning, there is must be a substantial inventory of nipples in terms of style and quantity in order to provide an acceptable arrangement of the flow control system downhole. A method of completing wells that would allow more use of standard completion equipment would make the completion process less expensive and would reduce the need for inventories of many different sizes and configurations of a given type of downhole equipment.
Packers are one commonly used type of completion equipment. A permanent packer is preferred over a temporary removable packer under a variety of conditions, including potentially hostile environments in terms of pressure, temperature and fluid exposure. The packer is expected to be in the wellbore for long periods of time. The permanent packer has certain advantages in terms of capacity and functionality in comparison to other types of packers. However, the permanent packer is difficult to remove from the wellbore, and attempting to do so typically requires a milling operation to remove an anchor, which involves significant planning and time. There are also semi-permanent packers which can be placed in a well but can also be retrieved without milling and destroying the packer, thereby potentially allowing the packer to be reused. A need exists for improved methods of removing permanent packers from wellbores.
Downhole alteration of completion equipment has been used only on a limited basis in the past. One common downhole alteration is the use of a jet perforating gun to form holes in the well casing, and thus create a flow path for hydrocarbons to pass from the formation into the wellbore. Another such technique that has been used is to cut slots in well casing by lowering a jet nozzle into a well and pumping a fluid through the nozzle radially outward against the casing, at a high enough pressure to cut holes or slots in the casing. One embodiment of this technique is described in U.S. Pat. No. 4,134,453. The above-described uses of downhole cutting or perforation of well completion equipment have not eliminated the need for many sizes and configurations of equipment such as landing nipples, packers, and a variety of downhole tools.
In general, there is a long-standing need for simpler and less expensive methods of completing wells.
The present invention relates to a method of machining a workpiece in a subterranean wellbore. The method comprising the steps of: (a) providing a workpiece that comprises (1) a first section that comprises a first material, and (2) a second section that comprises a second material, the second section forming at least one surface of the workpiece; (b) placing the workpiece in a subterranean wellbore that is surrounded by a geologic formation; and (c) machining the workpiece to remove at least part of the second material in the second section, so that at least one surface of the workpiece is formed into a desired configuration.
In some embodiments of the invention, the machining in step (c) substantially destroys the second section of the workpiece. xe2x80x9cMachiningxe2x80x9d in this context includes mechanical, electrical, and chemical techniques of removing material, as well as methods that involve combinations of these approaches. xe2x80x9cSubstantially destroysxe2x80x9d in this context means that the second section is reduced to small particles that can easily be pushed out of the way by a downhole tool or by a flow of fluid. In essence, xe2x80x9csubstantially destroyingxe2x80x9d the second section removes that section as a fixed structure, so that mechanical or other operations may take place in the space that was previously occupied by that second section. In this embodiment of the invention, the destruction of the second section can allow the retrieval of the remainder of the workpiece (e.g., a permanent packer) from the wellbore.
In another embodiment of the invention, the workpiece is a tubular member (e.g., a landing nipple) having a hollow axial bore therethrough and an opening at each end. Preferably, the first section comprises an outer tubular member having a hollow axial bore therethrough and having a inner surface and an outer surface. It is also preferred that the second section comprises an inner tubular member having an inner surface and an outer surface, and that the outer surface of the inner tubular member is in fixed contact with the inner surface of the outer tubular member. In other words, the inner tubular member and the outer tubular member are connected in a fixed manner to form a combined tubular structure.
In an especially preferred embodiment of the invention, the inner surface of the inner tubular member is cylindrical and has a substantially uniform inner diameter along its axial length prior to the machining in step (c). In other words, the inner surface presents a smooth profile to any downhole tools that are lowered past that surface. The absence of sharp edges or a complex profile of indentations helps prevent downhole tools from hanging up on the inner surface of the workpiece and provides a pressure barrier. When the time arrives to install a downhole tool in the workpiece, the machining of step (c) can remove at least part of the second material from the inner surface of the inner tubular member in a predetermined pattern, thereby forming a locking profile in the inner surface of the inner tubular member. xe2x80x9cLocking profilexe2x80x9d as used herein means a contour on the inner surface of the inner tubular member that comprises at least one locking recess. The locking profile will typically be adapted to engage locking members on a downhole tool. Preferably, the locking profile comprises a locking recess, a sealing section, and a no-go section that has a smaller inner diameter than the locking recess or the sealing section.
Thus, one embodiment of the present invention includes the additional step of placing a downhole tool in the axial bore of the workpiece and activating at least one locking member on the downhole tool to engage the locking profile on the workpiece, after that locking profile has been formed by the machining.
In another embodiment of the invention, the first section of the workpiece comprises a tubular member having a hollow axial bore therethrough and having an inner surface and an outer surface, and the tubular member has a plurality of apertures therein extending from the inner surface to the outer surface. Also in this embodiment, the second section comprises a plurality of closure members that seal the plurality of apertures in the tubular member. Therefore, in its initial state, the workpiece is a tubular member that has a solid wall all the way around its circumference. Then, when the time arrives to form one or more holes in the wall of this tubular member, the machining in step (c) can remove sufficient second material from at least one of the apertures so as to establish a path for fluid flow between the axial bore and the outer surface of the tubular member. Usually, the machining in step (c) is performed to open a fluid flow path through a plurality of the apertures.
The path for fluid flow (i.e., the hole opened by the machining) will often be located approximately at a depth in the subterranean wellbore from which hydrocarbon fluids are to be produced from the geologic formation into the wellbore. Alternatively, the path for fluid flow can be located approximately at a depth in the subterranean wellbore at which fluids are to be injected from the wellbore into the geologic formation.
The first and second sections of the workpiece can be made of a variety of materials, but preferably the second material is more readily removed by machining than the first material. The first material preferably comprises steel or other metal but may also be some form of carbide or ceramic structure. Suitable second materials include metals such as copper, brass, aluminum, nickel, or lead; and composites such as plastics, elastomers, or epoxies, with or without reinforcing fibers such as glass, carbon, Kevlar, or graphite.
The machining can be performed in a variety of ways. Examples of suitable machining processes include: contact abrasion or cutting by a rotating cutting member; electrochemical machining; electrical discharge machining; chemical machining; fluid jet milling; plasma milling; and laser milling. It would also be possible to use combinations of two or more of these processes, for example in a sequential manner. Preferably, the machining is performed by a downhole machining apparatus that is suspended within the bore of the workpiece by a structure selected from the group consisting of wireline, coiled tubing, electrical power cable, and combinations thereof.
Another aspect of the present invention is a downhole assembly that comprises a downhole workpiece located in a subterranean wellbore, the workpiece comprising (1) a first section that comprises a first material, and (2) a second section that comprises a second material, the second section forming at least one surface of the workpiece, wherein the second material is more readily removed by machining than the first material. The downhole workpiece can take a variety of forms, as outlined above. The assembly can also include a downhole tool located in the axial bore of the workpiece and comprising at least one locking member on the downhole tool that engages a locking profile on the workpiece.
Prior to installation of a downhole tool in engagement with a locking profile on the workpiece, the assembly can also comprise a downhole machining apparatus that is suspended within the bore of the workpiece by wireline, coiled tubing, electrical power cable, or the like.
The present invention can reduce the complexity of building, maintaining, and operating a well completion. It can permit the use and storage of fewer completion components for any particular well program. For example, the ability to custom machine a workpiece downhole reduces the need to maintain an inventory of similar equipment having many different configurations (i.e., landing nipples having different locking profiles). A separate benefit of some embodiments of the method is enhanced flexibility of the selected completion components by enabling more component functionality and by providing easier access to the components.
Downhole machining can permit the development of sophisticated completions with fewer inventory concerns and without creating complex tubular profiles before they are needed. For example, removing the complex profiles on the inner surface of wellbore tubular equipment reduces the locations where tools and flow control devices can get hung-up or located incorrectly. A smoother bore also reduces the locations where corrosion and scale have growth sites. The downhole machining method of the present invention can permit one or more of a wide range of activities, including destruction, retrieval, manipulation, and construction of completion components as needed.
The machining techniques can also provide means for manipulation or retrieval of completion components beyond conventional mechanisms. As one particular example, use of the present invention in a permanent packer can reduce the effort and increase the chances of success in attempting to retrieve this type of packer. In some embodiments, a packer of the present invention can be locked in place in a well, and a downhole tool subsequently can remove a selected portion of the packer.
The present invention can also increase the flexibility in building a flow control system in the completion, particularly with regard to the identification and location of landing nipples, the ability to create lock recesses of different sizes, shapes, and functions as required, and the eduction of inventory.